Two-piece tire

ABSTRACT

A two-piece tire assembly  10  with a removable tread belt  12  for installing about the circumference of a tire carcass  14  is provided. The two-piece tire assembly  10  includes a tread belt  12  has a belt structure  90  having two or more belt layers  100, 110, 120, 130  each layer having one or more belts. The tread belt  12  has a radially inner surface  70  having one or more protruding circumferential ribs  72  or grooves  74  that fit into complementary grooves  18  or ribs  19  on an outer crown surface of the tire carcass  14 . The tread belt  12  has a maximum axial belt width W at a radially inner surface. The carcass  14  has a maximum section width SW and ply line  20  having a maximum width P wherein W≦0.95P, BW≦5 0.85P and P&lt;SW.

FIELD OF THE INVENTION

This invention relates to pneumatic tires with removable tread belts andmore particularly, to very large, two-piece tires for heavy equipmentoperation.

BACKGROUND OF THE INVENTION

Very large two-piece tires, in which a removable tread belt is mountedupon a pneumatic structure, have been designed for use on largeearthmover vehicles. The large two-piece tires are subjected to highstress and loads under harsh environmental conditions such as in rockquarries, mines, foundries, and other areas where tires are subjected topuncture-producing and wear-inducing conditions.

Two engineering challenges separate the two-piece tires from standardone-piece tires. The first engineering challenge is to retain the outertread belt on the carcass, which requires enough interfacial pressurebetween the tread belt and carcass. The second engineering challenge isto ensure that the tread has adequate circumferential stillness torestrain the diametric growth of the carcass. The tread belt must alsohave enough flexural compliance to have a nonzero interfacial pressureat the leading and trailing edges of the footprint, and lowcircumferential compliance to compress the belt package in the footprintin the circumferential direction. These opposing requirements make itdifficult to design a two-piece tire which is utilized under heavy loadconditions.

With the continual drive to improve earthmover performance, there is acontinuing need to provide novel methods and tire designs for improvingearthmover tire durability. The present invention is directed to animproved pneumatic tire and removable tread belt assembly with which thefrequency of premature tire failure is thought to be substantiallyreduced while the overall useful life of the product is dramaticallyincreased.

SUMMARY OF THE INVENTION

A two-piece tire assembly with a removable tread belt for installingabout the circumference of a tire carcass is provided. The two-piecetire assembly includes a tread belt comprised of two or more beltlayers, each layer having one or more belts, wherein the tread belt whenviewed in a cross section has a maximum width W as measured at aradially inner surface of the tread belt. The tread belt includes onebelt layer having 0 degree cord angles relative to an equatorial plane(EP) of the tread belt and two belt layers having cords of opposite cordangles greater than 20 degrees, preferably in the range of 20 to 45degrees. An optional fourth top belt layer has cords oriented transverseor 90 degrees to the equatorial plane EP. The tread belt has theradially inner surface having one or more protruding circumferentialgrooves or ribs that fit into complementary grooves or ribs on an outercrown surface of the tire carcass. The width W of the tread belt whenassembled to the carcass is substantially narrower than the maximumsection width of the tire carcass. Preferably, the tire carcass has aradial ply cord reinforcement layer extending from a pair of bead coresin each sidewall across the crown of the carcass to form an inflated plyline. The inflated ply line has a maximum width P measured between thesidewalls at RhoM (radial distance corresponding to the maximum tiresection width) wherein the maximum width of the tread belt W is lessthan the width P, preferably less than 95 percent of P. This designconcept results in a stable tread supported by the pneumatic pressurewhen the footprint load is applied, eliminates the possibility of treadchunking at the belt edge and provides a superior cooler running tirewith improved wear rates. The reduced tread width truncates the outeredges of the tread belt where the interfacial pressure is very lowbetween the tread belt and the inflated tire carcass and eliminates thepossibility of gaps on either side of the tire's footprint. Thereduction in carcass shoulder gauge which accompanies the reduced treadwidth decreases the heat generation in the upper shoulder, reduces tireflexural deformations in the lower sidewall, improves durability in thebead area and reduces the possibility of chafing between tire and rim.

DEFINITIONS

The following definitions are controlling for the disclosed invention.

“Apex” means a non-reinforced elastomer positioned radially about a beadcore.

“Aspect ratio” of the tire means the ratio of its section height (SH) toits section width (SW) multiplied by 100% for expression as apercentage.

“Axial” and “axially” mean lines or directions that are parallel to theaxis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by the ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim.

“Bias ply tire” means a tire having a carcass with reinforcing cords inthe carcass ply extending diagonally across the tire from bead core tobead core at about 25-50 angle with respect to the equatorial plane ofthe tire. Cords run at opposite angles in alternate layers.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

“Chafers” refers to narrow strips of material placed around the outsideof the bead to protect cord plies from degradation and chafing caused bymovement of the rim against the tire.

“Chippers” means a reinforcement structure located in the bead portionof the tire.

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Flipper” means a reinforced fabric wrapped about the bead core andapex.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface under load and pressure.

“Inner liner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating gas or fluid within the tire.

“Net-to-gross ratio” means the ratio of the tire tread rubber that makescontact with the road surface while in the footprint, divided by thearea of the tread in the footprint, including non-contacting portionssuch as grooves.

“Nominal rim diameter” means the diameter of the rim base at thelocation where the bead of the tire seals.

“Normal inflation pressure” refers to the specific design inflationpressure at a specific load assigned by the appropriate standardsorganization for the service condition for the tire.

“Normal load” refers to the specific load at a specific design inflationpressure assigned by the appropriate standards organization for theservice condition for the tire.

“Ply” means a continuous layer of rubber-coated parallel cords.

“Radial” and “radially” mean directions extending radially toward oraway from the axis of rotation of the tire.

“Radial-ply tire” means a belted or circumferentially-restrictedpneumatic tire in which the ply cords which extend from bead to bead arelaid at cord angles between 65 and 90 with respect to the equatorialplane of the tire.

“RohM line” the RhoM line is defined as half way between the ply linebead pivot point BP and the ply line centerline C and in the preferredembodiment tire RhoM is coincident with the radial height at the maximumsection width U.S. Pat. No. 5,429,168 more fully describes and definesthe calculation of the RhoM line which is incorporated herein byreference in its entirety.

“Section height (SH)” means the radial distance from the nominal rimdiameter to the outer diameter of the tire at its equatorial plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a side view showing a prior art two-piece tire having linearor flat belts in the tread belt going over a flat ramp and emphasizesthe formation of gaps between the carcass and the tread belt close tothe leading and trailing edges;

FIG. 1A is a cross-sectional view of the prior art two-piece tire ofFIG. 1;

FIG. 2 is a graphical representation showing a schematic view of a priorart 45.00R57 2-piece tire assembly;

FIG. 3 partial plan view showing a prior art 45.00R57 two-piece tirecarcass with 25 psi inflation pressure;

FIG. 4 is a graphical representation showing the incremental forcerepresenting the effect of inflation pressure decomposed into itsvertical and horizontal components of an exemplary prior art 45.00R57two-piece tire assembly;

FIG. 5 is a graphical representation showing the gauge between the plyand the belt package of the exemplary prior art 45.00R57 two-piece tireassembly;

FIG. 6 is a graphical representation of interfacial pressure for theexemplary prior art 45 00R57 two-piece tire assembly calculated usingthe design drawings and plotted in for an inflation pressure of 132 psi;

FIG. 7 is a partial perspective view showing the hoop load distributionacross the prior art tread belt as shown in each end of the tread belt;

FIG. 8 is a graphical representation showing the hoop load distributionacross the belt package width of the exemplary prior art 40.00R57 treadbelt at 132 psi;

FIG. 9 is an exploded, cross-sectional view of a two-piece tire of thepresent invention;

FIG. 10 is an enlarged, cross-sectional view of the tread belt shown inFIG. 9;

FIG. 11 is an enlarged, cross-sectional view of half of the carcass ofthe tire carcass shown in FIG. 9;

FIG. 12 is a cross-sectional view of the assembled tread belt andcarcass forming a two-piece tire;

FIG. 13 is a graphical representation of interfacial pressure for theexemplary 45.00R57 two-piece tire assembly made according to the presentinvention, calculated using the design drawings and plotted in for aninflation pressure of 132 psi.

FIG. 14 is a graphical representation of the exemplary prior art40.00R57 tread belt under a realistic footprint load showing theundesirable effect of bending moment at unsupported edges of the treadbelt.

DETAILED DESCRIPTION OF THE INVENTION

Erosion of the interface between the tread belt and carcass in two-piecetires is a major design challenge. Erosion occurs when the shear stressbetween the tread belt and carcass exceeds a threshold value. Thisphenomenon can be expressed asMax. Shear Stress at Interface=μ*Interfacial Contact Pressure  (Equation1)where the coefficient of friction, μ is a function of pressure,temperature, and the contact medium (dirt, mud, water etc.). Slip occurswhen the left hand side of Equation 1 becomes greater than the righthand side. To delay the onset of slip and minimize erosion between thecarcass and tread belt, one must either reduce the shear stressdeveloped at the interface or increase the interfacial contort pressure.

The difference between the circumferential stiffness of carcass and thatof belt structure needs to be minimized to reduce the shear stressbetween the carcass and the tread belt. This is a challengingpreposition since the carcass must be compliant in the circumferentialdirection to be able to expand into the tread belt. Moreover, the treadbelt must have sufficient circumferential stiffness to stay on thecarcass and provide reasonable dimensional stability.

FIG. 1 shows a prior art two-piece tire 200 as defined in FIG. 1A with abelt structure 300 having linear or flat belt layers 302, 310, 320 and340 in the tread belt 212 going over a flat ramp and emphasizes theformation of gaps (G) between the carcass 214 and the tread belt 212close to the leading edge 400 and trailing edge 402 in the loaded tirefootprint. FIG. 1 suggests that the interfacial pressure at the leadingand trailing edges is very low if not zero.

According to the principles of tire mechanics, the maximum value oflongitudinal compressive strain in the footprint can be approximated asδ/3D, where δ is the tire deflection under the foot prim load and D isthe outer diameter of the tire. The carcass 214 of the two-piece tireassembly 200 is very compliant in the circumferential directionparticularly in the crown region 215 and can easily deform in thefootprint if compressive stresses are present. The tread belt 212,however, is relatively stiff in the circumferential direction especiallywhen a 0 degree belt is used. Therefore, the tread belt 212 can not becompressed as much as the carcass 214 in the circumferential direction.Shear stress develops in the footprint between the tread belt 212 andcarcass 214 as a result of this difference in stiffness. Under normaluse (with no breaking or driving torque acting on the wheel) the shearstress approaches its maximum value at the leading and trailing edges400, 402 and is zero at the center of footprint. The gap (G) between thetread belt 212 and carcass 214, outside the leading and trailing edges400, 402, clearly suggests the relative displacement at the interfacedue to the interfacial shear.

Relative movement between the carcass 214 and the tread belt 212 is notdesirable when the two surfaces are in contact since it produces wear.To minimize wear or erosion at the interface the left hand side ofEquation 1, the shear stress, has to be reduced at the onset of slip.Since the circumferential stiffness of the carcass 214 can not beincreased, the hoop stiffness of the tread belt 212 needs to beadjusted. The composite stiffness of the belt layers in thecircumferential direction can not be changed significantly if zerodegree belt layers are used.

To eliminate the possibility of slip and minimize erosion between thecarcass 214 and tread belt 212, one can either reduce the shear stressdeveloped at the interface below a threshold level or increase theinterfacial contact pressure. The structural fundamentals affecting theinterfacial contact pressure are described as follows.

Effect or Ply Line Ellipticity on Interfacial Pressure Distribution

FIG. 2 schematically shows a 45.00R57 two-piece prior art tire assembly.It gives the actual position of the ply line between the crown 215center and the mid sidewall 216 as well as the location of the 4 beltstructure 300. FIG. 2 also provides an elliptic fit to the ply line 220between the crown 215 center and mid sidewall 216 where the semi majoraxis of the ellipse is 19.6″ (one half the cavity width) and the semiminor axis is 13.6″.

The force per unit circumferential length pushing this quadrant of thecarcass 214 up, F₂, can be written in terms of the inflation pressureand the semi major axis of the ellipse asF ₂=(inflation pressure)*(19.6″)  (Equation 2)

The force per unit circumferential length pushing this quadrant of thecarcass 214 from left to right, F_(y), can be written in terms of theinflation pressure and the semi minor axis of the ellipse asF _(y)=(inflation pressure)*(13.6″)  (Equation 3)

Equations 2 and 3 suggest that F₂>F_(y). When the tire 200 is inflatedthe crown 215 region will expand and the mid sidewall will contractsince the ply length will not change significantly. A tread belt 212with high circumferential stiffness will restrict this ply lineexpansion in the crown and produce the interfacial contact pressure.

Thus, it is beneficial to have a ply line 220 with high ellipticity. Theamount of force exerted by the ply line 220 on the tread belt 212 isexpected to increase with increasing ply line ellipticity.

As the carcass 214 is inflated, it will exert a radial force on thetread belt which restricts the growth of carcass 214 in the crown area.Part of the inflation pressure will be conveyed from the ply 222 to thetread belt 212 depending on the geometry of the ply line 220 and therelative placement of the belt layers with respect to the ply line 220.Since the inflation pressure always acts perpendicular to the ply line220, the incremental force representing the effect of inflation pressurewill act perpendicular to the ply line 220 at any point along the ply222. The inflation pressure will push the ply 222 out and producetension in the ply cords 221.

The amount of compression developed outside the ply (e.g. between theply and the belt package) will depend on the amount of ply movement andthe level of constraint in the direction of ply movement. For example,the ply movement will not produce any compression in the sidewall region216 since the material outside the ply 222 is not constrained and it isfree to move.

The incremental force, representing the effect of inflation pressure canbe decomposed into its vertical and horizontal components as shown inFIG. 4. The vertical component of this force will push the ply 222 upand produce the interfacial compression between the ply 222 and thetread belt 212 as the ply 222 expands.

Compression can not be produced between the ply 222 and the tread belt212 unless the ply 222 moves closer to the tread belt 212 irrespectiveof the inflation pressure. Even though the ply line 220 expands in thecrown and contracts in the mid sidewall 216 as previously discussed, theply 222 will be assumed to grow uniformly for upper limit estimates ofinterfacial pressure. The vertical component of the ply growth if theply 222 was expanding by the same amount in all directions will bedefined as the “Vertical Pressure Coefficient”. As shown in FIG. 4 thevertical pressure coefficient can be calculated for these prior art flatbelt layers as:Vertical Pressure Coefficient=sin α  (Equation 4)Where “α” is the included angle between the tangent to the ply line 220and the line perpendicular to the belt layers at any point along the ply222.

This coefficient was calculated for a 45.00R57 sized two-piece tire andplotted in FIG. 4. The vertical pressure coefficient is 1.0 at thecenter of crown 215 and 0.70″ under the radially innermost belt edge 315of the belt structure 300 as shown in FIG. 4. It is important to notethat, the interfacial contact pressure between the carcass 214 and thetread belt 212 will decrease with decreasing Vertical PressureCoefficient.

Amount of compressive strain, ε, over a given distance “L” is ΔL/L whereΔL is the decrease in length due to compression. As shown in FIG. 5, thegauge between the ply 222 and the bottom belt 302 is not constant.

The radial distance between the top of the ply 222 and the bottom of thefirst belt 302 is 1.3″ at the crown center and 5.1″ under the belt edge315. Thus, to produce a uniform compressive strain (or a uniformcompressive stress) between the carcass 214 and the tread belt 212, theradial movement of the ply 222 under the belt edge 315 should be atleast (5.1/1.3) times higher than that at the crown center or equatorialplane EP. It should be noted that, the transverse constraint at thecenter of carcass 214 is much higher than that in the shoulder regionsince the upper sidewall 216 region can bulge out and relieve some ofthe compressive stress associated with the compressive deformation.

Note that reducing the tread belt width will bring the ply line 220closer to the belt layers under the belt edges 315, reduce the effectivegauge and increase the strain. Thus, lowering the radial distancebetween the belt edge 315 of the first belt 302 and the ply 222 of thetire carcass 214 will increase the interfacial contact pressure betweenthe carcass 214 and the tread belt 212 at the belt edge 315. Accordingto Equation 1, increasing the contact pressure will increase thethreshold for shear stresses at the interface and may eliminate thepossibility of slip between the carcass and tread belt at the lateraledges. The susceptibility of two-piece tire assemblies to interfacialerosion will be very low if slip is eliminated between the tread belt212 and the carcass 214.

The interfacial pressure between the carcass 214 and the tread belt 212is primarily controlled by the inflation pressure, ply line ellipticityand the belt package stiffness. The viscoelastic properties of compoundsbetween the carcass 214 and tread belt 212 can also affect theinterfacial pressure but these are secondary effects and will not beconsidered here.

The design geometry can be assumed to be close to the inflated geometryif the compounds between the ply 222 and the belt layers have enoughstiffness to stop rubber flow under compression, and if the beltstructure has enough circumferential stiffness to restrict the growth ofcarcass 214 due to inflation pressure. Considering these twoassumptions, the interfacial pressure, σ_(IF), can be approximated asσ_(IF)=(inflation pressure)*(VPC)*(L _(o) /L)  (Equation 5)where VPC=vertical pressure coefficient (see Eq. 4); L_(o)=radial gaugebetween ply 222 and first belt 302 at crown 215 center and L=radialgauge between ply and first belt 302 at a given point.

The interfacial pressure for the 45.00R57 two-piece assembly wasapproximated using representative tire dimensions and plotted in FIG. 6for an inflation pressure of 132 psi.

Note that, the interfacial pressure is 132 psi at the center of crownwhere the effect of inflation pressure is fully conveyed from the ply222 to the belt structure 300 and below 20 psi at the belt edge 315where VPC is relatively low and the gauge, L, is very thick.

When a two-piece tire assembly 200 is inflated, the carcass 214 expandsand exerts a radial force on the tread belt 212 producing theinterfacial pressure as discussed in the previous sections. Theinterfacial pressure pushes the tread belt 212 out and produces a hoopload distribution in the circumferential direction. The hoop loaddistribution is not uniform across the width of the tread belt 212 asqualitatively shown in FIG. 7.

The hoop stress is not uniform across the ring thickness either sincestiffer belts (with lower belt cord angles) carry more load andcompliant belts carry a smaller portion of the hoop load produced by theinterfacial pressure. Therefore, the hoop load per unit width will bemore useful than the hoop stress in tire design process.

The hoop load per unit width across the tread belt 212 can beapproximated asHoop load per inch=(σ_(IF)/2)*(128.2)  (Equation 6)where 128.2″ is the inner diameter of a 40.00R57 tread belt. Hoop loaddistribution across the tread belt width was calculated using theinformation provided in FIG. 6 and plotted in FIG. 8.

As shown in FIG. 8, the maximum load per inch is at the center of thetread belt 212 is equal to 8461 lb/in at 132 psi inflation pressure.

The load intensity decreases away from the center of the tread belt 212and goes below 1000 lb/in at the belt edge 315. The total load carriedby the belt structure 300 due to the inflation pressure can be found byintegrating the load distribution along the entire belt width. At 132psi the total load carried by a 45.00R57 tread belt 212 was calculatedas 210,594 lb. This approximate value is an upper limit based on twoassumptions introduced in the previous section. Thus, it is aconservative value and can be used to design tread belts for creep.

With this clear understanding of the general deformations and loadscreated by the use of a tread belt assembly 300 of two or more beltlayers has led to important insights into a greatly improved tread beltdesign structure.

FIG. 9 illustrates an exploded view of the cross-section of a two-piecepneumatic tire 10 of the present invention. While the invention wouldwork for smaller tires, it is more applicable to very large tires withrim diameters on the order of 35 inches and above. Further, thetwo-piece tire 10 of the present invention is designed for very large,heavy earth moving equipment and rough terrain. The tires 10 aretypically inflated to a high pressure, on the order of about 100 poundsper square inch (psi) or more with air, nitrogen or other appropriategas mixtures.

The improved two-piece pneumatic tire 10 of the present invention asshown in FIG. 12 includes a ground engaging, circumferentially extendingtread belt 12 mounted on a radially reinforced, beaded tire carcass 14.The details of the construction of tire carcass 14 and tread belt 12 aredescribed in more detail, below.

Referring to FIG. 11, one embodiment of a tire carcass 14 suitable forthe invention is shown. The carcass 14 preferably includes a radiallyouter surface or crown 15 having one or more circumferentiallycontinuous ribs 19 or grooves 18 for mating with aligned, opposinggrooves 74 and ribs 72 of tread belt 12. Preferably, the outer radialsurface 15 has a thin abrasion resistant compound layer 82 for forming alongwearing surface between the tread belt 12 and the carcass 14.

The tire carcass 14 generally includes a pair of tire sidewalls 16extending radially inwardly from the outer radial surface 15 of the tirecarcass and terminating in the vicinity of bead wires 22.

The carcass further includes an inner ply liner 26 that covers theentire interior facing surface 28 of the tire carcass 14 and serves tohold the gas mixture that is used to inflate tire 10 within the carcass.The carcass 14 further includes in its construction at least one rubberlaminated ply layer 34 of tire cord fabric which extends radiallyinwardly from the outer circumferential surface 15 of the tire carcass14, also called the crown area 15 of the tire carcass 14, and hasturn-up ends 34A which wrap or loop around a pair of bead wires 22. Thebead wire 22 preferably has a rounded bottom edge. Although the carcassply 34 is shown as being of single ply construction, a multi-plyconstruction can be employed if desired. Preferably, the carcass ply 34is made of a rubber laminated ply of steel cord, but it can be made of anon-steel carcass reinforcing material.

Between the inner liner 26 and the ply layer 34 is an optional barrierrubber layer 36 which backs up the entire length of ply layer 34 and isformed of a soft compound of rubber which squeezes against the ply layer34.

An optional steel chipper 40 wraps around the ply 34 and the bead wire22 and extends upwardly past the bead. The steel chipper 40 ispreferably surrounded by one or more optional chippers 42 for furtherreinforcement of the bead area. Adjacent the chipper and surrounding thebead area is an inner chafer 44 and an outer chafer 46. A chipper pad 50is located between chafer 46 and ply 34. A triangular shapedreinforcement member or apex 48 extends radially outward from the beaduntil about mid-sidewall. The apex 48 stiffens the bead area and helpsto prevent the tire sidewall from bending over the flange (not shown).

The ground engaging, circumferentially extending tread belt 12 isremovably mountable onto tire carcass 14. As best shown in FIG. 10, theunderside or inner circumference surface 70 of tread belt 12 comprisesone or more annular ribs 72 or grooves 74 that mate with correspondingaligned grooves 18 and ribs 19 of tire carcass 14. The mating ribs andgrooves function to position tread belt 12 with respect to the carcass14 during assembly. The tire tread belt 12 includes a tread portion 80on the outer radial surface for engagement with the ground.

The tread belt 12 further has a belt structure 90 having two or morebelt layers 100, 110, 120, 130 wherein each belt layer is preferablycomprised of steel cords. The invention is not limited to a particularwire construction, as there may be many wire constructions suitable foruse with the invention. Each tread belt layer 100, 110, 120, 130 maycomprise one or more belts.

The belt structure 90 may further include an optional outer layer 130which has the steel cords oriented at 90 degrees relative to thecircumferential direction.

EXAMPLE 1 Belt Package for a 42 Inch Wide Tread Ring

Belt layer Belt Angle Belt Type Cord Type Total Belt Width 100 +20single belt EP 39 110 0 single belt EP 37 120 −20 single belt EP 35 13090 single belt EP 34

The above chart describes an exemplary tread belt 12 having a beltstructure 90 comprising four belts 100, 110, 120, 130 and is shown inFIG. 10. Belt layer 100 is the radially innermost or first belt layer,the wire cords having a bias angle of 20 degrees. Belt layer 100 ispreferably the widest belt layer of all the layers. Belt layer 110 islocated radially outward and adjacent belt layer 100, and has a beltangle of 0 degrees. The 0 degree belt layer 110 is used to provide acircumferential constraint in order to control the diametrical growth ofthe tire 10. Belt layer 120 is a single belt located radially outwardand adjacent belt layer 110, and has a belt angle of −20 degrees. Beltlayer 130 is also a single belt located outward of belt layer 120, andhas a belt angle of 90 degrees. The four belt structure 90 is thuspreferably widest at the radially innermost belt layer 100, and has apyramidal structure with one inch belt stepoffs at the belt edge toeliminate high gradients in flexural stiffness in the radial crosssection. The belt structure 90 has three active belt layers 100, 110 and120 and two active belt interfaces designed to keep the hysteretic heatgeneration low and the operating tread ring temperature below criticaltemperatures.

The above describes a belt structure 90 comprising four belt layers.Belt 100 being the first layer is the radially innermost belt layer, andhas one or more belts having a bias angle range of 20 to 45 degrees. Iftwo or more belts are used in a layer, the belts are spaced apart a gapdistance. Belt layer 100 has a width in the range of about 40 inches. Asecond belt layer 110 is located radially outward and adjacent beltlayer 100, and comprises a belt angle of 0 degrees. One or more beltsmay comprise belt layer 110 and having a belt width about 38 inches.Belt layer 120 is located radially outward and adjacent belt layer 110,and has a belt angle range of −20 to −45 degrees, and a width in therange of about 36 inches. Belt layer 130 is located radially outward ofbelt layer 120, and has a belt angle of 90 degrees, and a width in therange of about 34 inches.

The interface between the tread belt 12 and carcass 14 in the aboveexample and description of the invention is such that an interferencefit occurs (the diameter of the tread belt is smaller than the diameterof the inflated carcass).

As shown in FIG. 12, the tread belt 12 and crown 15 of the carcass 14are designed such that the interface between the inner surface of treadbelt 12 and the outer surface of carcass 14 follows a relatively flatprofile. Preferably this flat profile has a maximum distance D_(O)between the axis of rotation and the radially inner surface of theradially innermost belt layer 100 as measured at the center orequatorial plane EP. The distance between the flat profile and the axisof rotation is constant as the point of interest moves away from theequatorial plane EP laterally outward on either side to the belt edge115 of the belt 100.

Optionally a radius of curvature of the tread belt 12 could be used andpreferably would follow the curvature of the ply line 20 maintaining aconstant distance between the radially innermost belt and the ply line.

The current invention claims a substantial improvement in tireperformance when the width W of the tread belt is substantially narrowerthan the maximum section width SW of the tire carcass. The inflated plyline has a maximum spacing between the sidewalls at RhoM (radialdistance corresponding to the maximum tire section width) wherein themaximum width of the tread belt W is proposed to be less than themaximum width of the inflated ply line P, preferably less than 95percent of P. The tread belt structure 90 has a belt layer maximum widthBW wherein BW is preferably less than or equal to 0.85P, allmeasurements being at normal inflation pressure and under no load.

This design concept results in a stable tread supported by the pneumaticpressure when the footprint load is applied, eliminates the possibilityof tread chunking at the belt edge and provides a superior coolerrunning tire with improved wear rates. The reduced tread width truncatesthe outer edges of the tread belt where the interfacial pressure is verylow between the tread belt and the inflated tire carcass and eliminatesthe possibility of gaps as is shown in the prior art FIG. 1 on eitherside of the tire's footprint. The gaps are reduced if not eliminated bythis enhanced mechanical fit which prevents getting any mud or debrisinto this area.

The reduction in carcass shoulder gauge which accompanies the reducedtread width decreases the heat generation in the upper shoulder, reducesthe flexural deformations in the lower sidewall, improves durability inthe bead area and reduces the possibility of chafing between the tireand rim.

As shown, the tread belt 12 at the innermost belt layers have a flatprofile to the inner surface 70 of the tread belt 12. Narrowing thetread belt width TAW and the width W results in much higher interfacialpressure between the lateral edges 115 of the tread belt 12 and theinflated carcass 14 because the edges 115 are substantially movedradially closer to the ply line 20. With reference to chart 13, agraphical representation of the interfacial pressure distribution acrossthe tread belt width of an exemplary tire 10 of the present invention iscalculated and plotted for an inflation pressure of 132 psi. As shown,when compared to the prior art tire 200 illustrated in FIG. 6, the tire10 of the present invention has a interfacial pressure distribution thatis substantially higher at the lateral edges 115 of the tread belt 12.This increase in interfacial pressure increases both the durability ofthe tire 10 and its ability to avoid slippage between the carcass 14 andtread belt 12 as the tire 10 enters and leaves the footprint on eachside of the contact patch. As a result the wear between these surfacescan be dramatically reduced.

As shown in FIG. 12, the belt structure 90 at the radially inner mostbelt 100 spaced a distance T_(O) between the ply line 20 and the belt100 at the equatorial plane EP. The radial distance T_(L) between theply line and the innermost belt increases across the axial width towardsthe lateral edge and reaches a distance T_(E) at the lateral edges suchthat T_(O)≦T_(E).

When compared to the prior art tire 200 having a T_(O)=1.3 inch at thecenter, as illustrated in FIG. 5 and T_(E)=5.1 inches at the lateraledge 315. Whereas the present invention tire 10 has T_(O)=13 inch at thecenter and T_(E)=2.5 inches at the lateral edges of the belt. Thisreduced distance T_(E) at the lateral edges 115 of the tread belt 12provides a higher interfacial pressure without changing the pressuredistribution as shown in FIG. 13. For this reason it is believed thatboth the performance and fatigue life of a tread belt 12 are greatlyimproved by the use of a narrower width W tread belt 12 on a flatprofile interface.

45.00R57 tires 10 made according to the present invention having areduced width W of the tread belt 12 and a corresponding narrow beltstructure 90 were molded. To simulate the reduced shoulder width in thecarcass 14 an existing carcass of the prior art tire 200 was modifiedwherein the shoulders were shaved or cut using a water jet to reduce amassive amount of rubber in each shoulder of the casing. This removedmaterial created a narrower width W of the carcass 14 to simulate thecarcass 14 of the present invention two piece tire. These tires werethen mounted on a vehicle and put into service. Decreasing the shouldergauge of tire 10 was found to reduce the heat generation of the casingduring normal use under heavy loads.

This reduction in tread width produced a slight increase in tiredeflection and created a significantly higher flexural deformation inthe upper sidewall where the gauge was reduced. Although, the flexuraldeformation was significantly increased the carcass was observed to runcooler in the upper sidewall region due to a significant reduction inrubber gauge.

Under comparable loading conditions the tires with reduced tread widthwere found to deform less in the lower sidewall region sincemid-to-upper sidewall region would deform significantly more compared tocontrol tires with wider tread width. As a result of reduced flexuraldeformation in the lower sidewall, the tires with narrower tread width12 exhibited a reduced occurrence of chafing in the bead area around therim and also improved ply ending durability of the carcass 14. Massiveamounts of rubber in the upper shoulder as illustrated in the prior arttire 200 generate high amounts of heat as they are flexed in and out ofthe footprint of the tire 200. This heat is transmitted throughout thetire carcass structure 214 and in particular can weaken the ply endingarea 34 or the belt package of the tread belt 12 in such a way that thetire durability or useful life can be reduced. By eliminating thisrubber, a significant reduction in heat buildup occurs in the carcass 14of the present invention.

The combination of reducing the width of the tread belt 12 and reducingthe gauge in the shoulder of the carcass 14 provides a footprint suchthat the tire 10 becomes more compliant in the upper sidewall butreduces deformations in the lower sidewall of the carcass 14 whichimproves fatigue durability in this region of the tire 10. The amount ofweight reduced in the carcass 14 alone can be more than 500 pounds usingthe present invention.

By reducing the tread width W up to 2.5 inches per side to 37.00 inchesas done in the experimental tire 10 from 42 inches of the prior art tire200 while the contact area under load is about the same means thefootprint length is increased while a corresponding reduction in widthof the footprint occurs. This means that basically the same contact areais supporting the load, but the load is supported over a longer length.Subjecting fewer tread elements to the compressive load but keeping themlonger in the footprint greatly reduces the hysteretic heat generationin the tread 80 and helps the tread belt run cooler. Additionally, byreducing the tread belt width W the interfacial pressure level at thelateral edges of the tread belt can be increased with no significantchange in interfacial pressure distribution. At the tread belt andcasing interface movement between the two components can generateerosion. By reducing the width W of the tread belt 12 such that it ismoved inwardly relative to the shoulders of the carcass 14, the lateraledges of the tread belt 12 are subjected to higher levels of interfacialpressure. As a result, the tread belt gaps G are eliminated andtherefore relative movement between the tread belt and carcass isdramatically reduced. This creates a tremendous benefit to improving thedurability of the tire 10.

When compared to the prior art tire 200, the edges of the tread belt 212are fundamentally unsupported, because the tread belt 212 extendslaterally beyond the carcass ply 34 and in some cases even overlaps theshoulder 216 of the carcass 214. This creates a cantilevered beam effectlaterally across the tread belt 212 wherein the tread belt 212 can flexupward and downward as the tire 200 enters and leaves the footprint.This is clearly shown in FIG. 14. This occurrence of flexure of thetread belt 212 may produce circumferential tread cracking at hingepoints and adversely affect the durability of the tread belt.

By reducing the width W of the tread belt 12 relative to the carcass 14as shown in the present invention, it is noted that the durability ofthe combination of a narrowed tread belt 12 and the reduced gauge in theshoulder of the carcass 14 can increase the useful life of the tire 10dramatically thereby reducing the operating costs and down-time to theowners of the vehicles which is a substantial improvement. Historicallythe prior art tread belt 212 was designed to be wider to help protectthe carcass 214, but in doing so it created a higher level of heatbuildup in the tread belt and the carcass which is known to bedetrimental to the durability of the entire tire structure. By reducingthe weight of the tire 10 by over 500 pounds it was shown that a slightloss in cut protection was a desirable compromise since the life of thetire 10 could be improved by over 500 percent in some cases.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed which will be within the full intended scope of the inventionas defined by the following appended claims.

1. A large two-piece tire assembly with a rim diameter of 35 inches ormore with a removable tread belt for installing about the circumferenceof a tire carcass comprises: a tread belt having two or more beltlayers, each belt layer having one or more belts; wherein the maximumwidth of a belt layer is BW and the radially innermost belt layer is thewidest belt layer; a tire carcass having a radial cord reinforced plystructure extending from a pair of bead structures across a crown of thetire carcass to form an inflated ply line; and wherein the tread beltand carcass when viewed in cross section have a width W and SWrespectively wherein the tread belt width W is less than the carcassmaximum section width SW and reducing the tread belt width lowers aradial distance T_(E) between the belt edge of the radially innermostbelt and the ply line and a radial distance T_(L) between the radiallyinnermost belt layer of the tread belt and the ply line increasesconstantly from T_(O) to T_(E) as the point of interest moves laterallyfrom an equatorial centerplane EP to the belt edge, T_(O) being theradial distance between the innermost belt and the ply line at thecenterplane EP and T_(E) being the radial distance between the innermostbelt edge and the ply line, and the interfacial pressure σ_(IF) can beapproximated as σ_(IF) (inflation pressure)*(VPC)*(L_(O)/L) where VPCequals vertical pressure coefficient; L₀ equals the radial gauge ordistance between ply and first or radially innermost belt at thecenterplane EP and L equals the radial gauge or distance between ply andfirst or radially innermost belt at a given point wherein L_(O) equalsT_(O) and L equals T_(L) and at the lateral edge is T_(E), T_(O) beingless than T_(E), T_(O) equals 1.3 inches at the center and T_(E) equals2.5 inches at the lateral edges of the belt for a 45 R 57 sized tire,wherein the tread belt width W is less than a maximum width P of theinflated ply line of the carcass and W≦0.95P, wherein each belt layer issubstantially parallel to the curvature of the inner tread surface ofthe tread belt and wherein the maximum width of a belt layer is BW andBW≦0.85P.
 2. The two-piece tire assembly of claim 1 wherein the treadbelt has one belt layer having 0 degree cord angles relative to anequatorial centerplane EP of the tread belt.
 3. The two-piece tireassembly of claim 2 where the tread belt has two belt layers havingcords oriented in opposite cord angles relative to the other belt layer,the cord angle being greater than 20 degrees.
 4. The two-piece tireassembly of claim 3 wherein the cord angle is in the range of 20 to 45degrees and the cord angles in each of the two belt layers are equal butoppositely oriented.
 5. The two-piece tire assembly of claim 3 whereinthe two belt layers are each adjacent the 0 degree cord layer one lyingradially above and the other radially below the 0 degree layer.
 6. Thetwo-piece tire assembly of claim 3 further comprises a fourth belt layerwherein the fourth belt layer has cords oriented at 90 degrees relativeto the equatorial plane. The fourth belt layer is radially outwardrelative to the other belt layers.
 7. The two-piece tire assembly ofclaim 1 wherein the tread belt has a radially inner surface having awidth W as measured across the inner surface excluding any ribs orgrooves for interlocking attachment to the tire carcass; and wherein theradially innermost belt layer of the tread belt at the equatorialcenterplane EP has a radial distance D_(O) as measured from the axis ofrotation and a radial distance D_(E) at each lateral edge of theinnermost belt layer as measured from the axis of rotation such thatD_(E) equals D_(O).